1. Field of the Invention
The present invention relates to a hydrogen sulfide and carbonyl sulfide removal apparatus using microwave plasma, and a method thereof. More particularly, the present invention relates to an apparatus and a method for removing poisonous gases, such as hydrogen sulfide (H2S) and carbonyl sulfide (COS), contained in natural gas, refined crude oil refinery gas, gasified synthetic gas, etc. by using microwave plasma, and generating elemental sulfur and hydrogen from the gases.
Especially, in the hydrogen sulfide and carbonyl sulfide removal apparatus using the microwave plasma, and the method thereof, since a synthetic gas, prepared through a synthetic gas preparation process in which under a reduced atmosphere, a sulfur-containing hydrocarbon material is partially oxidized by being mixed with steam or oxygen, includes large amounts of hydrogen sulfide and carbonyl sulfide, in order to remove the hydrogen sulfide and the carbonyl sulfide, gases of the hydrogen sulfide and the carbonyl sulfide are decomposed into elemental sulfur (S) and hydrogen (H2) by atmospheric plasma. Then, the decomposed elemental sulfur and the decomposed hydrogen are separately collected by a cyclone, thereby simplifying an additional step for collecting a combustible gas and elemental sulfur. Thus, it is possible to improve processing efficiency and economic efficiency.
2. Description of the Prior Art
Plasma, called the fourth state of matter, is an ionized gas where electrons and atomic nuclei are separated. While the plasma is formed, a large amount of radicals capable of activating a chemical reaction are formed. Plasma may be largely divided into low temperature plasma and high temperature plasma. The low temperature plasma may be used in the field requiring a chemical reaction at a low temperature of 100° C. or less. The high temperature plasma may be applied to the fields, such as incineration, and dissolution, requiring a high temperature because in the high temperature plasma, a temperature of 5000° C. or more can be reached in a short time. Also, application of the high temperature plasma technology in various fields from simple technologies such as incineration, and combustion to gasification technologies with processing efficiency and variable uses of generated gas have been recently researched. At present, the most widely used plasma method is a torch method using arc discharge. However, this method has a limitation in electrode life span due to a high temperature occurring during discharge, and requires a high electric power due to requirement of a large amount of current. Further, when steam for gasification reaction is injected, the electrode life span can be reduced. Accordingly, research on a high temperature plasma application technology using microwaves has been recently conducted.
Meanwhile, gasification refers to a process of converting a hydrocarbon-based material into a combustible mixed-gas such as hydrogen, carbon monoxide and methane by reaction with a gasifying agent such as water vapor, oxygen, hydrogen, carbon dioxide gas. Herein, beside the combustible mixed-gas, impurities such as hydrogen sulfide, carbonyl sulfide, ammonia, ash, unreacted soot and tar are produced, and exist together with the combustible mixed-gas. Synthetic gas including hydrogen and carbon monoxide may be applied to hybrid power generation through a fuel cell, a gas engine and a steam turbine, liquid fuel production and chemical drug production, in which the above mentioned impurities have to be necessarily removed. Especially, since the gasification reaction is performed under a reduced atmosphere, main components of a sulfur compound within the synthetic gas are hydrogen sulfide and carbonyl sulfide. Such hydrogen sulfide and carbonyl sulfide not only corrode a device but also are very harmful to a human body. Thus, they have to be removed before having an effect on a gas engine, etc. or being discharged into air.
In a conventional synthetic gas desulfurization system, a wet refining method for absorbing and removing a sulfur compound by using an absorbing liquid at a low temperature has been practically used and applied. Herein, a general acidic gas removal system includes a sulfur compound absorption tower, and a sulfur compound stripping tower. In a case of carbonyl sulfide, due to its low water solubility, it is difficult to directly remove the carbonyl sulfide through the wet refining method. Thus, carbonyl sulfide is converted into hydrogen sulfide through a hydrogenation (hydrolysis) process, and then removed. The hydrogen sulfide is removed from synthetic gas by using absorbent. Then, the hydrogen sulfide removed in the absorption tower is stripped in a regeneration tower and transferred to a Claus process where the hydrogen sulfide is converted into elemental sulfur. The converted elemental sulfur is sold as a high value-added material used for producing sulfuric acid, medicines, cosmetics, fertilizer and rubber product raw materials.
In a case of electric power generation using synthetic gas, from the point of efficiency view, high power generation efficiency can be achieved when gas at a high temperature is supplied to a gas engine and combusted. Accordingly, it is preferable that synthetic gas generated from a gasification reactor is subjected to removal treatment of hydrogen sulfide at a temperature as high as possible before being used for power generation.
However, in a case of a conventional commercially available synthetic gas desulfurization technology, since an absorption process is performed at a low temperature of 50° C. or less, synthetic gas at a relatively low temperature is supplied. Thus, power generation efficiency is low, three or more processes such as a hydrogenation process, an absorption tower, a regeneration tower for absorbent, and a Claus process for generating elemental sulfur are required, and the absorbent has to be periodically supplemented. In other words, the technology has a disadvantage in that a high process cost and a high amount of energy are required. Further, while the sulfur absorbent is in contact with the synthetic gas, a part of the absorbent may be scattered. Then, the scattered absorbent may be included in the synthetic gas and flowed into the gas engine, thereby causing gas engine corrosion and air pollution.
Accordingly, it is required to research a novel method for improving economic efficiency and removal efficiency of hydrogen sulfide gas by simplifying the above processes.